There's a photo I wish to heck I could find online to put here, but it's in b/w and of a grade crossing with two F or E units coming toward each other with a high-speed running meet, with the RR crossing sign almost exactly between them.
I think the phrase, "Once in a lifetime" doesn't do the photo justice. More like a "Once in a century" shot for all photographers, collectively.
I just wish I could find the shot I'm talking about. For a 'right place and right time' shot, I doubt anyone could ever beat it.